1. Field of the Invention
The present invention relates to a method and apparatus for applying flux for use in brazing aluminum or an aluminum alloy (which are collectively called as xe2x80x9caluminum materialxe2x80x9d) and is employed for in the manufacture of various products (for example, a radiator or a condenser).
The present application is based on Japanese Patent Applications No. Hei. 10-214485, 10-214488, 10-239172 and 10-239175, which are incorporated herein by reference.
2. Description of the Related Art
For example, in the case of manufacture of a heat exchanger from aluminum material, heat-transfer tubes made of aluminum material and radiation fins made of aluminum material are assembled, and the assembly is heated in a heating furnace, thereby fusing brazing filler metal (an aluminum alloy containing 5-16% Si) that is interposed beforehand between the heat-transfer tubes and the radiation fins. The heat-transfer tubes and the fins are brazed by means of the brazing filler metal.
In order to achieve high-quality brazing between the heat-transfer tubes and the radiation fins, fluoride-based flux is applied to the portions of the tubes and fins which are to be brazed, so as to fracture an oxide film covering the surface of the aluminum material constituting the heat-transfer tubes and the radiation fins.
The fluoride-based flux comprises 65.6-99.9 wt. % KAlF4 and 34.4 to 0.1 wt. % K3AlF6 and is commercially available under the trade name NOCOLOK FLUX.
A method of applying this flux is described in Japanese Patent Publication Nos. Hei. 1-143796, Hei. 3-275272 and Hei. 4-322896 or the like.
Japanese Patent Publication No. Hei. 1-143796 describes a method whereby flux can be applied solely to areas requiring coating by use, as a dispersion medium, of polybutene whose viscosity is greater than that of water and which sublimes with an increase in temperature. Japanese Patent Publication No. Hei. 3-275272 describes industrially efficient manufacture of an aluminum heat exchanger by coating of flux, which includes polybutene as a dispersion medium, to a traveling coating belt and by transfer of the flux to the surface of aluminum material from the coating belt.
Neither of these patent coatings specifically discloses correlation between the amount of flux added to polybutene and means for applying the flux. The former publication describes only the amount of flux added to polybutene but contains no description of a measure for applying the flux. The latter patent publication describes only means for applying flux and contains no description about the amount of flux added to polybutene.
Further, coating material of the above slime-like flux is applied primarily by manual paint with a brush. Accordingly, the amount of flux applied on the surface of a component becomes non-uniform, for example, such as on the tope peaks of a corrugated component used in the core of the heat exchanger. Further, during a painting process, flux is splashed, thereby staining surrounding facilities.
With regard to coating material formed by addition of flux into polybutene, the viscosity of the coating material increases with an increase in the amount of flux contained in the coating material. Consequently, coating material containing a small amount of flux has low viscosity and, hence is applicable to a spraying method or a dipping method. However, such coating material is not suitable for a transfer method employing an coating belt. On the other hand, coating material containing a large amount of flux has high viscosity and, hence can be applied to a transfer method employing an coating belt as coating means. However, such coating material is not suitable for a spraying method or a dipping method.
As mentioned above, in connection with the method of applying flux for use in brazing aluminum material, a close correlation exists between the amount of flux added to polybutene and means for applying the flux.
The present inventor found that most of the areas requiring coating of flux are narrow and that coating material doped with flux is required to have high viscosity for adherence to the narrow areas after coating. On the basis of this finding, the present inventor has completed the present invention.
Incidentally, a core of a heat exchanger, such as an evaporator or a condenser, employed in an automobile cooling system is usually constituted by stacking in an alternating manner a plurality of corrugated outer fins and a plurality of flat coolant tubes into a layer of required width. After the ends of the respective coolant tubes of the core are inserted into tube insertion holes formed in header tanks, powder flux or a flux solution is sprayed onto the overall core, whereby the flux adheres to the core. This core is then heated in a heating furnace, to thereby braze together the top peaks of the corrugated outer fins and the coolant tubes remaining in contact with the outer fins.
Flux adheres to areas of the core other than the areas to be brazed, thus wastefully consuming flux and disadvantageously adding to cost. Further, splashing of flux deteriorates the working environment and stains surrounding facilities.
An object of the present invention is to provide a method of applying flux for use in brazing aluminum material which enables coating of flux to only areas requiring coating of flux, enables stable holding of an amount of flux required for brazing in areas requiring coating, and improves the reliability of brazing.
Another object of the present invention is to provide a flux coating apparatus which can automatically and uniformly apply slime-like flux to the surface of a component and prevents staining of surrounding facilities, which would otherwise be caused by splashing of flux.
Still another object of the present invention is to provide a heat exchanger manufacturing method which prevents waste of flux, deterioration of the working environment, and staining of surrounding facilities, which would otherwise be caused by splashing of flux.
To achieve the object, according to a first aspect of the present invention, there is provided a method of applying flux for use in brazing aluminum material. The fluoride-based flux is uniformly dispersed and mixed in and with synthetic resin which has fluidity at room temperature (generally 20xc2x0 C. to 25xc2x0 C.) and sublimes at a temperature lower than a brazing temperature, to thereby constitute 40 to 70 wt. % of the mixture. The mixture is applied to coating belts which travel, and transferred to the surface of aluminum material.
The synthetic resin doped with flux has high viscosity and can stably adhere to areas on the coating belt and the surface of the aluminum material where the synthetic resin is transferred, without being removed.
The amount of flux added to synthetic resin is increased, so that the amount of flux required for brazing can be ensured by means of a small amount of coating material to be transferred. The amount of synthetic resin to be transferred can be reduced accordingly, to thereby increase a rate at which synthetic resin sublimes in a sublimation process before the brazing process and to save energy.
The synthetic resin doped with flux is transferred from the coating belts to the surface of aluminum material, and hence the synthetic resin is inevitably applied to the top peaks of aluminum material which are to be brought into contact with another aluminum material at the time of assembly. Consequently, flux can be applied to only the areas requiring coating.
Preferably, at least one side of the coating belt facing aluminum material is formed from elastic material which is deflected upon receipt of pressing force from the aluminum material at the time of transfer of the synthetic resin.
The coating belt is deflected at the time of transfer of the synthetic resin, to thereby cover, with the synthetic resin, the areas of aluminum material to be coated. Accordingly, synthetic resin doped with flux can be stably transferred from the coating belts to the areas of the aluminum materials to be coated.
According to a second aspect of the present invention, there is provided a flux coating apparatus. A pair of feed rollers is rotated in opposite directions while remaining in contact with each other, wherein an area above the line of contact between the feed rollers is taken as an inlet section for storing a slime-like flux. Dam members are provided along and remain in sliding contact with end faces on opposite ends of the pair of feed rollers so as to prevent the flux from flowing laterally from the inlet section. A pair of endless coating belts are spaced at a required interval so as to be mutually opposed in a vertical direction and which are rotated in opposite directions. At least one of the pair of feed rollers is in contact with at least one of the pair of endless coating belts, thereby transferring the flux to the surface of the endless coating belt. The surface of the endless coating belt coated with the flux comes into elastic contact with an introduced component to be coated with flux, to thereby coat the surface of the component with the flux during the course of feeding of the component in a single direction.
Preferably, each of the endless coating belts is provided with flux guides for collecting the flux adhering to the surface of the endless coating belts to a required width.
Preferably, the lower endless coating belt extends longer than does the upper endless coating belt in the direction from which the component is introduced, to thereby constitute a component inlet section for receiving the component 15.
The slime-like flux stored in an inlet section uniformly adheres to the surfaces of a pair of feed rollers as a result of rotation of the feed rollers, and flux is uniformly transferred from the surface of the feed rollers to the surfaces of a pair of upper and lower endless coating belts remaining in contact with the feed rollers. Flux can be uniformly applied to the surface of a component to be coated with flux which is introduced between and comes into elastic contact with the pair of upper and lower endless coating belts.
The surface of the component can be coated with flux without generating irregularities, thus enabling proper brazing of the component.
As mentioned above, flux can be automatically applied to the surface of the component by means of the endless coating belt, thus preventing splashing of flux and staining of surrounding facilities.
The flux adhering to the surface of the endless coating belts is collected to a required width by means of flux guides, thus preventing staining of surrounding facilities, which would otherwise be caused by the flux spreading to and falling from the side edges of the respective endless coating belts.
The component inlet section is provided on the lower endless coating belt so as to extend beyond the upper endless coating belt in the direction from which a component is introduced, and hence the component can be readily transferred to the component inlet section. Accordingly, a component can be readily and smoothly introduced between the upper and lower endless coating belts, thus efficiently coating the component with flux.
According to a third aspect of the present invention, there is provided another type of flux coating apparatus. A pair of endless coating belts are vertically spaced a predetermined interval so as to be mutually opposed. The coating belts are rotated in opposite directions and brought into elastic contact with the top peaks of a corrugated component to be introduced between a clearance between the opposing portions of the endless coating belts, and apply slime-like flux to the top peaks during the course of feeding the corrugated component in a single direction. A pair of presser plates presses the opposing portions of the endless coating belts against the top peaks of the corrugated component.
Preferably, a clearance between the pair of presser plates in the vicinity of a component inlet side is set so as to become sufficiently greater than the height of the corrugated component.
Preferably, the pair of presser plates are vertically adjustable.
In the flux coating apparatus according to the present embodiment having the foregoing configuration, when a corrugated component is introduced between a pair of upper and lower endless coating belts, the endless coating belts are brought into elastic contact with the top peaks of the corrugated component at a given, uniform contact pressure, and flux can be uniformly applied to the top peaks of the corrugated product during the process of feeding of the corrugated product in the direction designated by the outlined arrow.
The flux is prevented from being applied to the top peaks of the corrugated component in insufficient or excessive amount, thus enabling proper brazing of the corrugated component.
As mentioned above, by means of the presser plates the pair of endless coating belts are brought into resilient contact with the top peaks of the corrugated outer fin at a given, uniform contact pressure, thereby preventing deformation of the corrugated component.
The flux can be automatically applied to the top peaks of the corrugated component by means of the pair of endless coating belts, thus preventing staining of surrounding facilities, which would otherwise be caused by splashing of the flux.
The clearance between the pair of presser plates in the vicinity of a component inlet section is set so as to become sufficiently greater than the height of the corrugated component, thereby enabling smooth introduction of the corrugated component into the clearance between the opposing surfaces of the pair of endless coating belts and realizing smooth flux coating operation.
The presser plates are vertically adjustable. Vertical adjustment of the presser plates enables appropriate control of contact pressure at which the pair of endless coating belts are brought into contact with the top peaks of the corrugated fin, optimization of the amount of flux applied to the top peaks of the corrugated component, and reliable prevention of deformation of the corrugated component.
According to a fourth aspect of the invention, there is provided a method of manufacturing a heat exchanger. The slime-like is applied to the top peaks of corrugated outer fins. A plurality of outer fins and a plurality of flat tubes are stacked in an alternating manner, to thereby constitute a core having a required width. The ends of the tubes of the core is inserted into tube insertion holes of header tanks, and the core is heated in a heating furnace, thereby brazing together the top peaks of the corrugated outer fins and the tubes remaining in contact therewith.
Preferably, the slime-like flux is applied beforehand to either the peripheral edges of the tube insertion holes formed in the header tanks or the edges of the tubes, and at the time of brazing of the outer fins and the tubes through heating in the heating furnace, the peripheral edges of the tube insertion holes of the header tanks and the ends of the respective tubes are brazed.
According to the present invention, assembly of the core of a heat exchanger involves application of the slime-like flux to solely the top peaks of the corrugated outer fins which are stacked with the coolant tubes of the condenser core in an alternating manner and must be brazed. The areas other than those required to be brazed are not coated with the flux, thus eliminating wasteful consumption of the flux and enabling advantageous manufacture of the core at reduced cost.
As mentioned above, the flux 10 is applied to solely the top peaks of the outer fins 4. Further, slime-like flux comprising resin material as a dispersion medium is used, there can be prevented deterioration of the working environment and staining of surrounding facilities, which would otherwise be caused by splashing of the flux 10.
Further, the slime-like flux is applied beforehand to either the peripheral edges of the tube insertion holes formed in the header tanks or the edges of the coolant tubes to be inserted into the tube insertion holes. Simultaneously with brazing of the outer fins and the coolant tubes through heating in a heating furnace, the peripheral edge of each of the tube insertion holes of the header tanks and the ends of the respective coolant tubes are brazed, thus improving work efficiency and productivity in manufacture of a heat exchanger.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.